For example, Japanese patent No. 2853207 (hereinafter referred to as document 1), Japanese patent application publication No. 2011-50163A (hereinafter referred to as document 2), and Japanese patent application publication No. 2011-29067A (hereinafter referred to as document 3) disclose wireless power supply systems (contactless power supply systems) configured to supply a lighting load with electric power in a non-contact manner. Such a wireless power supply system includes a power transmission unit and a power reception unit. The power transmission unit includes a power transmission coil to which an AC power is supplied. The power reception unit includes a power reception coil which receives an electric power from the power transmission unit through an electromagnetic induction due to an AC magnetic field generated by the power transmission coil in a contactless manner.
Document 1 discloses a power supply system including a power supply transformer and a communication transformer. The power transmission coil and the power reception coil are composed by the power supply transformer. The power transmission unit supplies the power reception unit with an electric power through the power supply transformer in a non-contact manner. The power reception unit transmits a feed-back signal to the power transmission unit through the communication transformer in a contactless manner. Herein, the feed-back signal includes information with respect to a current flowing through a lighting load, a voltage of the lighting load, and the like. The power transmission unit adjusts the supply power to the power reception unit according to the feed-back signal received from the power reception unit.
Document 2 discloses a wireless power supply system for supplying an LED element with an electric power in a contactless manner. Document 3 discloses a lighting apparatus to which an electric power is supplied in a contactless manner.
In the conventional wireless power supply system, it is possible that supply power to the lighting load becomes unstable, because an output voltage of the power reception coil varies due to: a load change caused by a temperature character, an age-related deterioration or the like; a relative position gap (misalignment) between the power transmission unit (power transmission coil) and the power reception unit (power reception coil); and the like.
The power supply system disclosed in Document 1 performs a feed-back control between the power transmission unit and the power reception unit by use of the communication transformer. However, in this system, it is possible that the feed-back signal cannot be transmitted correctly due to: a variation in windings of the communication transfer, a positional misalignment between a primary side and a secondary side of the communication transformer, or the like. In these cases, output voltage of the power reception coil may fluctuate, and it is possible that supply power to the lighting load becomes unstable.